1. Field of the Invention
The present invention relates to a method for lifting a membrane separation device which is immersed in liquid to be treated so as to obtain permeated water through a filtration membrane.
2. Description of the Related Art
A water treatment device such as a membrane separation device disposed in a treatment tank is typically provided with a chain for lifting. A lifting apparatus is operated so as to lift up and down the membrane separation device after a hook of the lifting apparatus is engaged with a portion of the chain above the water.
Japanese Patent Laid-Open Application No. 2001-255305 discloses a lifting method using a lifting apparatus provided with a reference portion to be referenced when the lifting apparatus is positioned in a treatment tank, where the lifting apparatus includes a main body portion capable of moving up and down along with a water treatment device, a coupling portion capable of engaging with and disengaging from a hanging portion of the water treatment device, and a positioning portion for positioning the main body portion to the reference portion so as to align the coupling portion with the hanging portion of the water treatment device.
In accordance with the above-mentioned lifting apparatus, a membrane separation device can be accurately operated from outside of the treatment tank when the membrane separation device is immersed into the liquid to be treated and invisible from outside of the treatment tank.
However, in the above-mentioned lifting method, it is necessary for the lifting apparatus to be provided with a complicated mechanism in order to engage the hook or the like of the lifting apparatus with an engaging portion of the membrane separation device which is immersed in the liquid to be treated and thus invisible from outside of the treatment tank, which disadvantageously increases the initial cost and the maintenance cost of the lifting apparatus.
In addition, a conventional method of manually engaging the membrane separation device and the lifting apparatus requires highly complicated and cumbersome operations. It is also problematic that a separate liquid suction mechanism and a liquid storage mechanism are necessary to lower the liquid level of the treatment tank and expose the membrane separation device above the liquid surface.
Furthermore, since the chain and the like provided to the membrane separation device is also immersed into the liquid to be treated along with the main body, it may be corroded after a long-term use in the vicinity of an interface of the liquid surface such that the membrane separation device may not be properly lifted up using such a corroded chain.